Solid-state lighting is an attractive alternative to incandescent and fluorescent lighting systems for a wide range of lighting applications because of its relatively higher efficiency, robustness, and long life. However, conventional solid-state lighting systems featuring light-emitting diodes (LEDs) have a number of limitations related to thermal management of heat generated by the LEDs and the need to control the distribution of light and ensure low glare.
In many lighting applications it is desirable to have lighting systems or luminaires that are thin, low-volume, and lightweight in order to meet certain aesthetic design requirements or so that the lighting system is unobtrusive. In other applications it is desirable to be able to conform the illumination source to a curved surface. Current LED systems generally include LEDs that are operated at relatively high current and thus very high brightness. High-current operation is often preferred in order to reduce the LED count and thus reduce the overall cost of the lighting system. However, this results in the generation of significant amounts of heat that must be extracted from the LED. In contrast to incandescent lamps, which radiate heat into the environment, the heat from LEDs in large measure must be extracted by conduction, which generally requires relatively large amounts of material with a high thermal conductivity, such as metal core printed circuit boards (MCPCBs), heat sinks, and in some cases active (e.g., forced-air) cooling. Such thermal-management solutions typically are not sufficiently flexible to permit conforming to curved surfaces, and they take up significantly more space than the LEDs themselves, resulting in increased size and volume of LED-based lighting systems. These solutions may also increase system cost and potentially reduce reliability and operational lifetime of the lighting system. The high junction temperatures associated with high-current operation also reduce LED lifetime.
Furthermore, if not appropriately managed, high-brightness illumination sources do not provide the desired light distribution pattern and may produce significant and unacceptable levels of glare. Such optical challenges have been addressed in a number of ways. For example, many lighting systems utilize a diffuser in front of the LEDs, but in order to effectively reduce pixelization (i.e., the visualization of the individual LEDs), the diffuser must have relatively low transmittance, which decreases efficiency. Some lighting systems utilize a large mixing volume for the emitted light, which increases the size and cost of the illumination system, or utilize relatively sophisticated and costly optics to control the light-distribution pattern.
Thin, low-volume, and lightweight lighting elements are also beneficial from a building design and cost perspective. Virtually all buildings require unoccupied space to support heating, ventilation, and air conditioning (HVAC) systems, electrical and communications wiring, plumbing, and other facilities. From a cost perspective it is desirable to minimize this unoccupied space, which often results in these spaces becoming very crowded and densely packed, which can lead to difficulties in initial installation and subsequent repair and modification of the systems within the space. In some construction processes, lighting is installed closer to the end of the project, in which case the unoccupied spaces may already be substantially filled, resulting in significant installation difficulty. Lighting systems that require significant volume in the unoccupied space may thus increase the building cost by requiring additional unoccupied space, or pose installation challenges if sufficient space has not been allotted in advance.
Space constraints also apply in building renovation. In these cases the spacing between floors is generally fixed and cannot be changed. In particular, many older buildings were not designed to support the required range of facilities in more modern buildings. More unoccupied space can sometimes be created, but typically at the expense of the occupied space, for example by reducing the ceiling height.
In view of the foregoing, a need exists for systems and techniques enabling the low-cost design and manufacture of compact, reliable, high-brightness lighting systems having low glare and the ability to produce different light-distribution patterns.